Drilling and completing an underground well, e.g., an oil well penetrating an underground formation containing oil or other fluids, sometimes require perforating a portion of a well tubular and a formation followed by gravel packing the well. The perforated tubular and gravel packing allow production of formation fluid while consolidating loose formation materials and helping to prevent formation caving.
Perforating a well is typically accomplished during well completion operations using a conventional perforating gun or similar tool. A plurality of explosive cartridges, shaped charges or other tubular and/or formation penetrating means are used to create holes in the tubular wall and/or formation at a location proximate to a producing zone or other formation of interest.
A fluid or fluid-like substance having a density greater than water is typically used in the wellbore during completion of a well, e.g., a heavy weight drilling mud and water mixture is typically used to create a "kill" fluid. The dense mixture in the wellbore typically produces overbalanced hydrostatic pressures within the wellbore (as compared to nearby formation fluid pressures) that minimize the risk of excessive gas entering the wellbore from a formation.
A viscous entraining fluid or fluid mixture (such as a brine) may also be used during gravel packing operations to entrain gravel particles and carry the stabilizing particles as a slurry into the face of a sandy formation to form the gravel pack. Fluid loss control measures may also be required during a conventional packing process, e.g., using fluid additives to control lost circulation (e.g., LCM "pills") during gravel packing.
Conventional packing processes typically use separate gravel packing tools or other means for placing particulates in the well and/or formation. Gravel packing tools are typically run into the well after the tubulars are perforated and perforation tools have been removed from the well. Backflushing tools for removing excess sand or gravel slurry, coiled tubing, and an associated kick fluid supply (e.g., compressed nitrogen or other gases) may also have to be run into the well after packing in order to clean out viscous fluids and to "kick" or bring a conventionally gravel packed well into fluid production.
Similarly, the conventional process of perforating typically requires separate tools and process steps. Again, removal of dense completion fluids may subsequently be required.
Although some of these process steps are intended to remove potentially damaging fluids and other materials from the well, some portion of these materials tends to remain in the permeable portions of the formation, such as a productive interval. This can damage the productive interval, e.g., by promoting swelling and loss of permeability of a clay-containing formation. Damage to a productive interval may only be shallow (e.g., "skin" damage) and relatively easy to correct, but the damage may also be more extensive and permanent.
In addition to the risk of damage to the formation, significant costs are typically required for a drilling rig or other well intervention unit to be on-site during conventional perforation and packing processes. Rig equipment is typically used periodically throughout both processes, e.g., to supply completion fluids and to support equipment during many "trips" that are required during the processes to place, support, reposition, activate, and/or remove perforating and packing tools.
Although combination perforating and gravel packing tools are known in the art, they also typically require a drilling or workover rig (or other well intervention unit) to be on site and a tubular work string or other apparatus within the well to support the tools in a first position, unsupport the tools, move the tools, and emplace the tools in a second position. The rig and tubular string are also typically used to support and provide completion fluids, slurry, or other fluids to the combination tools.